Radiation is the transfer of heat or energy from a hot surface to a cold surface through air or a vacuum. For example, radiant heat from the sun travels through space and strikes the roof of a building and exterior walls of a building, causing the roof and exterior walls of the building to increase in temperature. Heat flows from the outer surface of the roof and exterior walls of the building to inner surfaces of the roof and the walls of the building through conduction. If the inner surfaces of the roof and walls of the building are warmer than surfaces inside the building that are spaced apart from the roof and inner walls of the building, heat will radiate from the inner surfaces of the roof and the walls of the building to the surfaces inside the building. Radiation between surfaces inside a building occurs through invisible infrared heat rays.
Heat can also exit a building through radiation. In winter months, surfaces inside a building are often warmer than the inner surfaces of the walls and the roof of the building. Warmer surfaces inside the building radiate heat to the inner surfaces of the walls and the roof of the building, causing them to increase in temperature. This heat flows from the inner surfaces of the walls and the roof of the building to the outer surface of the walls and roof of the building through conduction.
The ability of a material to emit radiant energy and absorb radiant energy are defined by the materials emissivity and reflectivity. The lower the emissivity of a material, the lower the amount of heat that is radiated from its surface. The higher the reflectivity of the material, the higher the percentage of incident radiant heat that is reflected from the material's surface. Radiant barriers and reflective insulation systems reduce radiant heat transfer between surfaces across open spaces, which is a significant contributor to heat gain during warm months and heat loss during cold months. Radiant barriers are a single layer of reflective material spaced apart from a surface which radiates heat. Radiant barriers do not prevent heat on one side of the reflected material from being conducted to the second side of the reflective material. Reflective insulation systems are typically laminate products that reduce heat transferred due to radiation, as well as convection. Reflective insulation systems typically include a reflective layer and a conduction preventing layer. The conduction preventing layer prevents heat on the reflective layer of the reflective insulation system from being conducted to the second side of the reflective insulation system.
Reflective insulation systems are installed such that a reflective layer is spaced apart from the roof decking or the outer wall of a building. Heat that is radiated inward from the roof or outer walls of the building is reflected off the reflective layer of the reflective insulation system back to the roof or outer surface of the building. The temperature of the roof or outer surface of the building increases rather than the interior of the building.
In winter applications, heat radiated by surfaces in the interior of the building are reflected back into the interior of the building if a reflective layer is included that faces the interior of the building. By reflecting radiant heat from the roof and external walls of the building back to the roof and outer walls of the building the heat that enters the building is reduced during warm months. By reflecting the heat radiated by the interior surfaces of the building back to the interior surfaces of the building, the heat that escapes from the building is reduced during cold months.
Several reflective insulation systems currently exist. One reflective insulation system includes two layers of aluminum separated by one or more layers of plastic bubbles or plastic foam material. An example of a reflective insulation system having a central layer formed of a plastic foam material and two outer aluminum foil layers is described in U.S. Pat. No. 5,316,835 to Groft et al. The layers of this reflective insulation system are heat or flame laminated together into a single insulative construction. Another existing reflective insulation system includes a layer of aluminum foil bonded to a layer of plastic bubbles or foam material and a layer of polyethylene vapor barrier bonded to the layer of plastic bubbles or plastic foam material. One significant problem with existing reflective insulation systems is that the layer of plastic bubbles or plastic foam is highly flammable. The flammability of the layer of plastic bubbles or foam greatly limits the number of applications this type of reflective insulation system can be used in.
Typically, reflective insulation systems which use plastic bubbles or foam material as the center layer bond the layer of plastic bubbles or foam material to the two layers of aluminum foil or layer of aluminum foil and layer of polyethylene by heating the materials to fuse them together. This process restricts the types of vapor barriers that can be used in these reflective insulation systems. Most notably, polyethylene or polypropylene vapor barriers that are least flammable cannot currently be used in these reflective insulation systems, since they do not readily bond by heating and fusing. The vapor barriers that can be bonded by heating and fusing are more flammable, adding to the flammability problem.
Water-based adhesives have been used to laminate insulation products in the past. Water based adhesives must dry out to properly cure and create a strong bond between the facing and the insulation. Water-based adhesives work well for laminating insulation that has facing on only one side and when a thick layer of insulation is used, because the adhesive is able to thoroughly dry.
Water-based adhesives would not work well for laminating a thin layer of insulation between two layers of facing, since the air movement around the adhesive is very restricted. The restricted air movement around the adhesive would greatly increase the time required for the water-based adhesive to cure and may even prevent the adhesive from ever properly curing.
If a water-based adhesive freezes before it properly dries, the water-based adhesive will never properly cure and will not provide a sufficient bond between the materials being glued together. This is especially problematic in cold weather climates. Insulation products are often loaded onto trucks that are exposed to the cold weather a short time after a layer of facing is laminated to the insulation, potentially allowing the adhesive to freeze before a it can properly cure.
There is a need for a reflective insulation system that comprises a layer of fiberglass insulation bonded between a reflective layer and a vapor retarder layer by a hot melt glue or other adhesive that is able to properly cure when airflow is restricted. Such a reflective insulation system is significantly less flammable than existing reflective insulation systems.